1. Field of the Invention
This invention relates to a process for use in the construction of integrated circuit structures. More particularly, this invention relates to a process for etching an accurate thickness of oxide from an oxide surface of an integrated circuit structure on a semiconductor substrate using a nitrogen plasma and a rf bias applied to the substrate.
2. Description of the Related Art
In the construction of an integrated circuit structure on a semiconductor substrate, an oxide material, such as silicon oxide, is the material of choice for providing insulation or dielectric material between electrically conductive portions of the integrated circuit structure. The silicon oxide insulation material is normally formed as an oxide layer over other portions of the integrated circuit structure, and the oxide layer may then be subsequently patterned to form the desired shape. Alternatively, portions of oxide may be individually formed over segments of the underlying integrated circuit structure using masks to isolate such portions of oxide from the remainder of the integrated circuit structure, e.g., the formation of field oxide between transistor areas. In either case, the formation of the oxide on the integrated circuit structure is usually carried out either by deposition of silicon oxide on the integrated circuit structure, e.g., by chemical vapor deposition (CVD); or by growth of the silicon oxide, e.g., growth of silicon oxide on an exposed silicon surface, e.g., by oxidation of the silicon using water vapor.
As integrated circuit structures have continued to shrink, both in size of individual components as well as in spacing between such components, it has become necessary to accurately control the thickness of such silicon oxide portions formed on the integrated circuit structures. For example, formation of an MOS transistor may require the formation of a high quality gate oxide of less than 2.5 nanometers (nm) in thickness. This formation of very thin oxide layers has become increasingly difficult to accomplish using conventional deposition or growth processes when thin oxide layers of accurate and uniform thickness are required.
It would, therefore, be useful to provide a process for the accurate and reproducible removal of controlled thicknesses of silicon oxide from a previously formed silicon oxide portion or layer of an integrated circuit structure on a semiconductor substrate.
In accordance with the invention, a reproducibly accurate and uniform amount of silicon oxide can be removed from the surface of an oxide previously formed over a semiconductor substrate by exposing the oxide to a nitrogen plasma in an etch chamber while applying an rf bias to a substrate support on which the substrate is supported in an etch chamber. The thickness of the silicon oxide removed in a given period of time may be changed by changing the amount of rf bias applied to the substrate through the substrate support.